The effects of diabetes mellitus during cooling on ACh- and KCl-induced responses were investigated in rat urinary bladder. Diabetes was induced in the rats by 50 mg/kg streptozotocin via an intraperitoneal injection. Rats’ body and bladder weights were measured. The isometric tension to ACh (10–9 – 3 × 10–4 M) and KCl (5–100 mM) in strips of urinary detrusor muscle of diabetic and non-diabetic rats, in organ baths at 37 and 28ºC were recorded. The body weights were significantly decreased and the bladder weights increased in STZ-induced diabetic group compared to the non-diabetic group. ACh and KCl caused concentration-dependent contractions of urinary bladders from non-diabetic and STZ-induced diabetic rats. During cooling, the sensitivity and the maximal response were significantly higher than those during 37ºC, both in non-diabetic and diabetic preparations. Cooling of detrusor muscle preparations induces a graded contraction inversely proportional to the temperature in diabetic rats. It may be assumed that the cooling response involves the same mechanisms in the diabetic and non-diabetic animals.
The properties of mechanical responses elicited by stimulation with acetylcholine (ACh) were investigated in circular smooth muscle preparations isolated from the proximal colon of guinea-pig. Application of ACh (10–8–10–6 M) for 3–5 min produced a biphasic response, with an initial contraction followed by a relaxation. Atropine inhibited the initial contraction, while Nω-nitro-L-arginine (L-NA) inhibited the relaxation, suggesting that the former was produced by activation of muscarinic receptors while the latter was produced by an elevated production of nitric oxide (NO). In the presence of atropine, the ACh-relaxation was attenuated by removal of the mucosa and abolished by removal of both submucosal and mucosal layers. The ACh-induced relaxation was also attenuated by either tetrodotoxin (TTX, 3 × 10–7 M) or hexamethonium (10–6 M). In the presence of atropine, transmural nerve stimulation (TNS) elicited a biphasic response, with an initial phasic contraction followed by a relaxation. The amplitude of TNS-induced relaxation was significantly reduced by hexamethonium or L-NA and was abolished by TTX. Both ACh and TNS produced relaxation in preparations isolated from the proximal colon, but not in those from the middle part of colon. Immunohistochemistry for neuronal nitric oxide synthase revealed no difference in the distribution of nitrergic nerves between the proximal and middle part of the colon, with nitrergic nerves in both the mucosal and submucosal layers as well as in the smooth muscle and myenteric layers. These results suggest that ACh induces NO production by excitation of postganglionic nerves distributed mainly in the mucosal and submucosal layers. In circular smooth muscle preparations isolated from the middle part of colon, ACh or TNS produced contractile responses alone, with no associated relaxation, suggesting that the ACh-activated postganglionic nitrergic nerves are distributed in the mucosal and submucosal layers of the proximal colon but not in the middle part of the colon.
Purpose: The objectives of this study were to compare the functional expression of muscarinic and purinergic receptors in the urinary bladder of 2 species, rat and guinea pig under comparable experimental conditions; and to test whether the receptors in males and females differ. Methods: Reverse transcription-polymerase chain reaction (RT-PCR) techniques were used to identify gene expression profiles in bladder smooth muscle (total n=8 rats, 7 guinea pigs) and mechanical responses to nerve stimulation and applied acetylcholine (ACh) in the presence of specific antagonists were used to identify functional receptor sub-types (total n=12 rats, 16 guinea pigs). Results: RT-PCR indicated that M2 and M3 were the predominant muscarinic receptor genes in both the male and female rat and guinea pig bladders. The phasic component of the nerve-induced contraction was greater in guinea pigs vs. rats. The tonic component and the ACh response were inhibited by the M3 receptor antagonist, darifenacin (10–6 M, P≤0.05), but not by the M2 receptor antagonist, methoctramine (10–5 M). The antipurinergic drug α, β-methylene ATP (5 × –5 M) caused a significant reduction in the amplitude of the phasic response to nerve stimulation in all groups, and this effect was significantly greater in male vs. female rats. mRNA for the purinergic P2X1, P2X2, P2X4, P2X5 and P2X7 receptors was detected in both male and female rats, whereas P2X3 and P2X6 were inconsistently detected in male rats. The P2X1 purinoceptor antagonist pyridoxal-5’-phosphate-6-(2’-naphthylazo-6’-nitro-4’, 8’-disulphonate) (PPNDS), only inhibited nerve induced contractions at high concentrations (up to 10–4 M). Conclusions: While only minor functional differences were documented in cholinergic and purinergic bladder contractile responses between male and female animals, and between rats and guinea pigs, data such as presented in this study are critical in determining how relative functional contributions may change in the diseased state, providing valuable information towards new treatment options.
RhoA, a small GTPase, is one of the key proteins of smooth muscle contraction. In allergic asthma, an upregulation of RhoA in bronchial smooth muscle has been suggested. However, the mechanism of its upregulation has not yet been clarified. In the present study, the effects of interleukin-4 (IL-4), one of the T-helper 2 cytokines, on RhoA mRNA expression and promoter activity of RhoA gene were examined in cultured human bronchial smooth muscle cells (hBSMCs). The quantitative real-time RT-PCR analyses revealed that incubation of hBSMCs with IL-4 (10, 30 and 100 ng/mL, for 24 hr) caused an increase in RhoA mRNA in a concentration-dependent manner. In luciferase reporter gene assay using hBSMCs that were transfected with luciferase constructs and were then stimulated with IL-4 (100 ng/mL), an importance of the most proximal STAT6 binding region (78–70 bp upstream of the transcription initiation site) was suggested. It is thus possible that IL-4 is capable of upregulating RhoA by promoting its transcription in hBSMCs. The proximal STAT6 binding region is required for the IL-4-induced increase in promoter activity of the human RhoA gene.